Electronic control apparatus for motors



Feb. 17, 1948. s, s5 s 2,435,966

ELECTRONIC CONTROL APPARATUS FOR MOTORS F 119d Mal 0h 2 $1168 hS-Slleet l (1076/1415 Bnventor (Ittorneg s. cs. ISSERSTEDT 2,435,966

Feb. 17, 1958.

' ELECTRONIC} CONTROL APPARATUSTOR morons 2 Sheets-Sheet 2 Filed March 26, 1943 Patented Feb. 17, 1948 ELECTRONIC CONTROL APPARATUS FOR MOTORS Siegfried G. Isserstedt, Toronto, Ontario, Canada, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application March 26, 1943, Serial No. 480,668

11 Claims. 1

The present invention is concerned with motor control apparatus designed to provide a novel motor control system of the type in which the energization of the motor is controlled by an electronic discharge device.

An object of the present invention is to provide a motor control system of extreme sensitivity in which an electronic amplifier is employed to control the motor and in which the effect of a normal controlling voltage on the input circuit of the amplifier is periodically changed in magnitude.

A still further object of the invention is to provide such a system in which the control voltage is a cyclically varying voltage such as an alternat ing voltage.

A further object of the invention is to provide such a system in which the control voltage is periodically increased in magnitude by an abrupt voltage peak without introducing transient effects.

A still further object of the invention is to provide such a system in which the effect of'the control voltage is gradually changed in magnitude.

A still further object of the invention is to provide such a system in which the effect of the controlling voltage is perlodically increased and then decreased.

A still further object of the invention is to provide such in which the voltage applied to the input circuit of the amplifier is supplied by an impedance bridge and varies in magnitude and phase with the relative values of the impedance in said bridge.

A still further object of the present invention is to provide such a system in which a plurality of electronic amplifiers are employed and in which the effect of the normal controlling voltage on the input circuits of both amplifiers is simultaneously varied.

A still further object of the invention is to provide an extremely sensitive amplifier in which the magnitude of a biasing voltage is periodically varied so as to vary the magnitude of the signal voltage required to cause operation of the amplifler.

Other objects of the invention will be apparent from a consideration of the accompanying speciflcation, claims and drawing, of which Figure 1 is a schematic view of one form of my motor control system;

Figure 2 is a diagrammatic view indicating the I relationship between the grid and plate voltages of the system shown in Figure 1,

Figure 3 is a schematic view of a modified form of my motor control system, and

Figure 4 is a diagrammatic view indicating the relationship between the grid and plate voltages of the system shown in Figure 3.

Referring to Figure 1 of the drawing, themotor associated with the motor mechanism to be controlled is indicated by the reference numeral Hi. This motor may be any conventional form of direct current motor which continuously rotates in one direction upon a direct current being passed therethrough. The motor in is designed to form a driving unit 01' a servo motor assembly having a reduction gear train and clutches for causing a driven shaft to be driven in one direction or the other. For purposes of simplicity, the mechanism including the gear train and clutches has not been shown but is merely designated by the reference numeral ii. These clutches are in the form of a pair of electromagnetic clutches, one or the other of which is energized, The e1eCtro magnetic windings of these clutches are designated in the drawing by reference characters i2 and I3. When winding I2 is energized, one clutch is engaged and the motor is effective to rotate a shaft l4 in one direction. When electromagnetic winding i3 is energized, on the other hand, the other clutch is engaged and the shaft I4 is rotated in the opposite direction, The motor 10 and the assembly ll together constitute a motor means functioning to provide reversible motor action. Any other suitable reversible motor arrangement could be employed. The shaft i4 is connected to a suitable controlled device I 5 which illustratively might be the operating mechanism for an airplane rudder. The shaft is also connected to a contact arm i 6 of a control potentiometer ll. The contact arm I8 is adapted slidably to engage resistance element i 8.

The current flow through electromagnetic windings l2 and I3 is controlled by a pair of electronic discharge tubes 2| and 22, In the particular application which I contemplate, I have found it desirable to employ gas filled tubes although it is to be understood that the invention is not so limited. The tube 2| comprises an indirectl heated cathode 23 having a heater 24, a control grid 25, a shield grid 25, and an anode 27. Similarly. the tube 22 comprises an indirectly heated cathode 29 having a heater 30, a control grid 3i, a shield grid 22 and an anode 33. The tubes 2| and 22 may be of any suitable gas filled type. I have found the type 2050 gas filled tube particularly desirable for this purpose. In the particular application contemplated, I have found 65 it desirable to connect the shield grids 2B and 32 3 to their associated cathodes 23 ductors 34 and 35.

The operation of the tubes 2I and 22 is controlled by an impedance bridge including the potentiometer I1 previously described and a control potentiometer 38. This control potentiometer comprises a resistor 39 and a slidable contact 48. The slidable contact 48 is adapted to be positioned by any suitable controller 4| to which it is connectedlby a link 42. The controller 4I may illustratively'be the gyroscope in an aircraft for controlling the position of the rudder in order'to keep the aircraft on the course for which the yroscope is set. The right hand end of resistor 39 is connected to the right-hand end of resistor I8 by conductor 43, a rheostat 44, and conductors 45 and 48. The left-hand end of the resistor 39 is similarly connected to the left-hand end of resistor I8 by conductor 41, a rheostat 48, and conductors 49 and 58. A further rheostat 52 is connected between the junction of conductors 49 and 58 on the one hand and the junction of conductors 45 and 45 on the other. The rheoand 28 by coneter I1.

eluding potentiometers I1 and 38 by a step-down transformer 51. This transformer comprises a high voltage primary 58 and a low voltage secondary 59. The low voltage secondary 59 is connected across resistors I8 and 39 and serves to supply power to the bridge. Theright-hand end of the secondary is connected directly to the right-hand end of resistor 39 by conductors and 82. The left-hand end of secondary 59 is connected to the left-hand end of winding 39 by conductor 63, a condenser 64 and conductors 85 and 88. A resistor 61 is connected between the relation with respect to the anode voltage.

The output voltage of the bridge is impressed across a center-tapped resistor 18.. The slider 48 is connected by a conductor II to the upper terminal of resistor 18 and the contact arm I5 is connected by a conductor 12 to the lower end of resistor 18. The upper end of resistor 18 is in turn connected by conductors 13 and 14 to grid 25 and the lower end of resistor 18 is connected by conductors 15 and 15 to grid 3|.

Condensers 18 and 19 'are connected between the grids and cathodes of the two tubes 2| and 22. The condenser 18 is connected between grid and cathode 23 by conductors 14, 88, condenser 18, and conductors 8I, 82, 83 and 84. The condenser 19 is connected between grid 3i and cathode 29 by conductors 18, 88, 81, 82, 83, and 88. The function of condensers I8 and 19 is to filter out any high frequency voltage impulses. Due to the extreme sensitivity of tubes 2I and 22, a. very slight voltage impulse on the grid might serve to cause the tube in question to discharge when such discharge is not desired. By providing condensers 18-and 19 any such voltage impulse, which is usually extremely short in duration, is by-passed through the condenser. The

'biasing means for the grids 28 and 32 is connected between the center tap 98 and conductor 82 leading to the cathodes 23 and 29. This biasing means will be described presently.

Power is supplied to the system by a pair of batteries 92 and 93 connected in series. Where the control system of the present invention is employed in connection with an airplane, the batteries 92 and 93 may each be 12 volt batteries.

The battery 92 is employed to energizea motor unit 95 of a voltage converting device which is capable of transforming direct'voltage into alternating voltage ofa desired frequency. A typical unit of the type which I employ is that known 10 under the trade-name of Genemotor. Such devices employ a single rotor and a plurality of windings one of which acts as a field winding for the direct current motor and the other of which has induced in it an alternating current of the desired frequency. For convenience of illustration, the motor and generator units are shown as though they were a separate motor and generator and have been designated by reference numerals 95 and 96. The battery 92 is connected go to the generator unit 95 by conductors 91 and 98. The motor and generator units of the voltage converter are secured toa shaft 99. This shaft is in turn connected to the high speed end of a gear train I88. The lower speed end of this gear g5 train is connected to a shaft IM to which is Power is supplied to the impedance bridge in-l secured a rotary contactor disk I82. This disk for a short arcuate portion I88 of conductive material, this arcuate strip of conductive material ductive strip l,83./ Cooperating with the outer 35 track are brushes I88. I89 and H8. These brushes are spaced apart a distance such that the three being connected by a conductor I81 to th con-f brushes'successively engage the conductive strip I88 for short periods during approximately 188 degrees of the complete '360 degrees f rotation 40 of the disk. During the remaining 330 degrees,

the three brushes are all engaging portion of the disk.

The rotary contactor I82 is employed to control the connections. of brush I84 to points at various potentials with respect to the potential of the cathodes. Apair of potentiometers H2 and II 3 are connected across battery 92. Potentiometer H2 comprises a resistance H4 and a sliding contact H5. The potentiometer H3 comprises a resistance H1 and a sliding contact H8. The upper ends of the resistances H4 and H1 are connected to the positive end of battery 92 by conductors I28, I2I, I22 and I23. The lower end-s of resistors I I4 and H1 are connected to the negative end of battery 92 by conductors I25, I26, I21, I28, I29, I38 and I3I. It can be readily seen that the upper ends of resistances I I4 and H1 of potentiometers I I2 and H3 are connected to the positive terminal of battery 92 and the lower ends to the negative terminal.

A condenser I35 is connected to slidable contact H5 and through conductor I25 to the lower terminal of potentiometer H4 so as tobe in parallel with the lower portion of resistance H4. A

e insulating I I8 and the lower terminal of resistor H1.

A plurality of choke coils I48, I41 and I42 similar condenser I38 is connected between tap I49 serve to bleed off any charge on condensers 15 I43, I44 and I45 as soon as-they are discon- -nected from a source of power. They have relatively high resistance values in order not to shunt the condensers appreciably.

Connected in series with brush I04 is a rheostat I50. This rheostat comprises a resistor I5I and a slidable contact I52.

A resistor I54 and a resistor I55 of a rheostat I56 are connected in series with battery 53. The rheostat I56 comprises, in addition to the resistor I55, a slidable contact I51. The

resistors I54 and I55 are connected In series with battery 03 by conductors I59 and I3I.

Operation 24, conductor I69, filament heater 30, and conduotors I10, 62, I61, I63, I29, I and III back to the negative terminal of battery 92. In spite of the fact that the motor I0 is running and tubes 2I and 22 are ready for operation, howeven'no movement of the shaft I4 takes place due to ,the fact that both windings I2 and I3 are deenergized. This is due to the fact that since the 'resistance bridge comprising potentiometers I1 and 30 is balanced no voltage is impressed across resistor 10. The grids 25 and iii are both biased negatively by the potential existing across the right-hand end of resistor I 55 which is introduced between the grids and cathodes by the following circuits. Considering first the grid 25, this grid is connected to cathode 23 by the fol? lowing circuit: from grid 25 through conductors 14 and 13, the upper end of resistor 10, tap 90. conductor I65, contact I51, the right-hand portion of resistor I55, conductors m, I63, m, 02, as, and 84 to cathode zaI Grid :1 is connected to cathode 20 by the following circuit: from grid 3i through conductors 16 and 15, the

lower portion of resistor 10, tap 90, conductor I65, slidable contact I51, the right-hand end of resistor i and conductors I30, I63, I61, 82, 03 and 80. It will be noted that, as previously indicated, the right-hand portion of resistor I55 is connected in series between the grid and cathode of each tube, the right-hand end of the resistor being connected to the cathodes and the left-hand end to the grids. Inasmuch as the right-hand end of resistor I55 is connected to the positive end of battery 03 and the left-hand end through resistor I54 to the negative end of battery 03, the connection of the right-hand portion of resistor I55 between the grids and cathodes serves to bias the grids negatively by a voltage equivalent to that existing across the right-hand portion of the resistor I55. The magnitude of this voltage can be initially adjusted by adjusting the position of slidable contact I51.

As far as the connections of resistors I54 and I 55 across battery 93 are concerned, the lefthandend of resistor I55 will assume a potential intermediate the potentials existing at the positive and negative terminals of the battery 03, the value of this potential depending upon the relative values of resistors I54 and I55. Due

to the rotary contactor I02 and the various connections' described; however, the potential of the left-hand end of resistor I55 is periodically changed for short periods of time. As long as the brushes I00, I08 and H0 are engaging the insulated portion of the outer track I05, the rotary contactor I02 does not affect the potential of the left-hand end of resistor I55. This condition will exist during half of each revolution of contactor I02. The gear train I00 is so selected that there is one revolution of contactor I02 during each six cycles of the alternating voltage generated by generator 96. Thus, the brushes I06, I09 and H0 are in engagement with the insulated: portion of the outer .track I05 during three of each six cycles of the alternating voltage applied to the output circuits of tubes 2i and 22 and to the impedance bridge which supplies the controlling grid voltage. Thus, during three of the six cycles the biasing voltage is unai'l'ect'ed by the contactor I02. When, however, the rotating contactor has moved to a portion such that the brush IIO engages the conductive arcuate portion I06, a circuit is estab lished between the positive terminal of battery 02 and'the left hand and of resistance I55 as follows: from the positive terminal of battery 02 through conductors I23, I22 and I19, condenser I45, inductance I42, conductor I80, brush IIO, conductive strip I66, conductor I01, conductive strip I03, brush I 04, conductor I12, contact I52 to the right-hand portion of resistor I5I, and conductor I 14 to the left-hand end of resistor Il6. The establishment of this connection tends to connect the left-hand end of resistor I05 te the positive terminal of battery 02. Since the cathodes and 29 are connected tothe negative end of battery 92, it will be obvious that any such tendency tends to raise the potential of the grid with respect to the cathode by an amount dependent upon the setting of rheostat I50.

{This raise in potential will take place very abruptly sincewhen the connection is initially established, the condenser I45 is discharged and offers substantially no impedance to the flow of current. The result is that the voltage applied to the grid rises very quickly. Almost immediately, the voltage starts to drop again because of the impedance oifered to the flow of current through the circuit Just traced by the condenser I45 as it becomes charged. The result is that there is a quick rise in grid voltage and a relatively quick drop creating a peak in the biasing voltage. The tendency is for this peak in the grid voltage to be extremely sharp. While it is desirable to have a voltage peak of relatively short duration, it is undesirable for this voltage change to occur too rapidly. If the voltage change is too rapid there is a danger that transient voltages may be introduced in the system. Such transient voltages, due to the extreme sensitivity of the gas filled tubes, may lead to one or both of the tubes becoming conductive at times when they should not be conductive.

The inductance I42 acts to prevent a too rapid change in the grid voltage and hence to prevent such transient voltages being introduced into the system. The effect of the inductance I 42 is to round the tops of the voltage peaks. 7

After a very brief interval, the conductive strip I06 will move from engagement with brush H0. The length of conductive strip I 06 is sufficient for the voltage peak to be substantially terminated before brush H0 and conductive I06 are separated. After a period of time corresponding to the aesaeoe length of one complete cycle of the grid voltage,

the conductlve strip I will engage the brush I09. When this happens, a connection will be established between tap H8 and the left-hand end of resistor I55 as follows: from tap III through conductor I18, condenser I, inductance HI, conductor I11, brush I09,-conductive strip I08, conductor I01, conductive strip I02, brush I04, conductor I12, contact I52, resistor I5I, and conductor I14 to the left-hand end of resistor I55. It will be noted that the slidable contact H8 is at a potential intermediate in value between the positions at the positive and negative terminals of battery 92. As a result, there is a tendency for the grid voltage again to be raised abruptly. This increase in the grid voltage will, however, be less than in the case previously described when conductive strip I05 was engaging brush IIO. Again, there will be a voltage peak, the duration of which is determined by the charge or condenser I. As in the preceding case, the

inductance Ill serves to prevent this voltage from changing too abruptly.

At the end of a period oi time equal in length to a cycle of the grid voltage, the conductive strip I05 will move into engagement with brush I08.

. When this'happens a circuit will be established between contact H5 and the left-hand end of resistor I55 as follows: from slider I I5 through conductor I10, condenser I40, inductance I40, conductor I1I, brush I00, conductive strip I05, conductor I01, conductive strip I03, brush I08, conductor I12, contact I52, resistor I5I and conductor I14 to the left hand end 01 resistor I55. While the potential 01 tap H5 is considerably lower with respect to the positive terminal of battery I92 than slider ill, it is still at a higher potential than the positive terminal or battery 92 and at a very much higher potential than the negative terminal of battery 03 to-which the lefthand terminal of resistor- I55 is normally connected. Thus, the establishment 01 this connection tends to raise the potential of the left-hand terminal of resistor I55 and hence to raise the potential or the grid voltage. The condenser I" serves to limit the duration of the voltage peak and the inductance I40 to limit-a sharpness of the voltage peak.

During the next three cycles of, r d voltage, the brushes I08, I09 and III willbe in engagement only with the insulating portion of the outer track so that the grid voltage will be constant.

It will be seen from the foregoing description that during three cycles of the grid voltage, voltage peaks are superimposed upon the grid voltage, these peaks being of relatively short duration and decreasing in magnitude in succeeding cycles. During the next three cycles, the grid voltage is constant. The various values of the voltage peaks are so selected that in the absence oi an unbalanced potential at the resistance bridge, neither of the grids 25 and, I2 is raised above the cut-oil potential. In other-words, as long as the bridge is perfectly balanced it is not desirable for either tube 2| or 22 to discharge.

The operation of the resistance bridge will now be considered. As previously indicated, the transformer 51 is employed'to supply power to this bridge. The primary 55 of the transformer is connected to the output terminals of the alternating current generator 96 as follows: from the generator 96 through conductors I82 and I84, primary winding 58, and conductors I85 and I85 to the other terminal or the generator 98. This connection serves to impress across the primary 8 winding an alternating voltage. As a result, the secondary 59 is energized to impress an alternating voltage on the bridge.

As long as contact members 40 and I6 occupy corresponding positions with respect to their associated resistors 39 and I8, no voltage exists across the output terminals of the bridge. This is on the assumption that rheostats 44 and 48 are set in the same positions. Let it be assumed that the condition to which controller 4| is responsive now changes in such a manner as to cause slider 40 to move to the right with respect to slider I8. Under these conditions, an unbalance voltage exists across the bridge, which voltage will be impressed across resistor 10. Furthermore, this voltage is such that during the half cycle in which anodes 21 and 33 are positive, the potential of the upper end of the resistor 10 is higher than the potential at the lower end. The result of this is that the potential of grid 25 tends to be raised with respect to cathode 29 and the potential of grid 3| tends to be lowered with respect to cathode 29.

If this unbalance in the bridge is very slight, as may well be the case, the slight amount of voltage change may not be suillcient to overcome the biasing efiect introduced by the potential existing across the right-hand end of resistor I55 when the left-hand end is at its normal potential. As previously explained, however, the grid potential is periodically increased momentarily. This is graphically shown in Figure 2 in which the numeral I90 is employed to indicate the Potential existing between the anode and cathode during the conductive half cycle and in which the reference numeral I9I indicates the grid voltage. For clarity of illustration, the amplitude of the grid voltage has been somewhat distorted and it is assumed that the cut-off potential is cathode potential rather than a value somewhat below cathode potential as would normally be the case. The peaks superimposed onthe grid voltage by operation of the contactor I02 are designated by the reference characters I92, I93 and I94. It will be noted that during the first six cycles of plate voltage in the diagram, the normal grid voltage, due to the combined effects of the normal biasing potential and the unbalanced voltage of the bridge and disregarding the voltage peaks I92, I93 and I94 is not sufiicient to cause the grid potential to rise above the cut-oil value. During these six cycles, however, the unbalance of the bridge is suificient so that when the peak I92 is superimposed on the grid voltage the grid voltage is raised above the cut-off value so as to render the tube in question conductive. With a gas filled tube such as employed in "the present system, the tube remains conductive after it has once become so, as long as the voltage is applied to the anode circuit. Consequently, the tube will discharge during the entire cycle. During the next cycle,

'in which .the peakv Ellis superimposed on the grid voltage the total grid voltage is at no time above=the cut-oil point so that the tube remains non-conductivef'Since the voltage peak I94 is even less in magnitude, the tube will also be nonconductive during the next cycle. Since no voltage peaks are applied during the next three cycles the tube will continue to be non-conductive during the next three cycles, v

The first two cycles of a second series of six cycles are shown in Figure 2. It is assumed in connection with the second series that the unbalance of the bridge is slightly greater. Under these conditions, the amplitude of the grid voltage "I is greater so that the grid potential is above the cutofl value during both of the first of the two cycles. Under these conditions, the third cycle would still be non-conductive and, of course, during'the succeeding three cycles, the tube would be non-conductive. If the unbalance were slightly greater, it will be obvious that the tube would be conductive during the first three cycles and nonconductive during the last. If the unbalance were still greater so that theamplitude of the grid voltage disregarding the peaks I92, I93 and I94 was sufficient to bring the grid potential always above the cut-off value, the tube would be conductive during every cycle of the anode voltage.

It will be noted that the phase relationship between the grid and plate voltages is such that the maximum value or the grid voltage occurs in an early portion of the cycle of anode voltage. The

advantage of this is that during those cycles in movement of the control device before the syswhich the tube is conductive, it is conductive over the greater portion of the cycle. This desirable phase relationship is obtained by means of condenser 64 and resistor 81, which are suitably proportioned to give the desired phase shifting effect.

Referring back to Figure 2, it will be noted that in the first cycle of plate voltage, the grid voltage is of sufficient magnitude as to cause the grid potential to exceed momentarily the cut-ofl value so as to render the tube conductive. The same condition exists during the first two cycles of the second group of cycles of plate voltage, In the case which has been considered, the upper end of resistor 10 is positive with respect to the lower end as a result of the unbalance o! the bridge.

Consequently, the potential or the voltage applied to grid is in phase with the plate current so that tube 2| is the onewhich will be rendered conductive during the first cycle of the first six cycles of plate voltage considered. When this occurs, current will flow through tube 2i and winding I3 as follows: from the upper terminal of generator 96 through conductors I82 and I98, winding l3, conductor I96, anode 21, cathode 23, and conductors 84, 83, 82, I61, I63, I30, I3I, 91,

I98, and I86 to the other terminal'of generator 96. The establishment of this circuit causes winding I3 to be energized with the result that one of the two clutches of mechanism II is engaged. The engagement of this clutch will cause shaft I4 to rotate in such a direction as to move the control device I5 in a predetermined direction and to move the contact arm I 8 in a clockwise direction. The movement of contact arm I8 in a clockwise direction will cause the bridge to be rebalanced with the result that the magnitude of the A. C. unbalanced voltage gradually decreases. When the bridge is completely balanced, the voltage applied to grid 26 will be merelythe total biasing voltage consisting of the normal biasing voltage as represented by the line I89 and the peak voltages I92, I93 and I94. Thisbiasing voltage never assumes a value sufilciently high to cause the tubes to discharge. Thus, the tube 2I will again become non-conductive so that winding I3 is deenergized and further movement of controlled device [5 and contact arm I 6 is terminated. By proper adjustment of the system, the amount of movement 0! the control device will correspond in any desired manner to the tem is rebalanced. Because of the fact that rheostat 82 is in parallel with potentiometer 12, the rebalancing effect of potentiometer II depends upon the setting of rheostat 52. Obviously, the lower the total impedance of rheostat 82, the greater will be the current flow through the lower portion of the bridge. This will increase the voltage drop across the resistors of rheostats 44 and 48 and decrease the voltage drop across resistor I8. The lower the voltage drop is across resistor I8 as compared with that across resistor 39, the greater will be the necessary movement or contact arm It in order for the system to be rebalanced. Conversely as the resistance value of impedance 82 is increased, the effect of potentiometer I1 is correspondingly increased so that a smaller adjustment of arm I8 is necessary. The two impedances 44 and 48 are provided for adjusting the position of the control device with respect to the controller. It the sliders of both impedances are moved towards the left, the bridge will be balanced when contact arm I8 assumes a position electrically to the left of slider 48. When the sliders of both rheostats 44 and 48 are moved to the left, the bridge will be rebalanced when contact arm I8 assumes a position electrically to the right of slider 40. Thus by adjusting rheostats 44 and 48, the control device may be caused to assume any position for any given value of the controlling condition.

Let it be assumed now that instead of the condition changing in such a manner as to cause contact 49 to be moved to the right, it changes in such a manner as to cause it to be moved to the left. Under these conditions, it will be obvious that the unbalance voltage is disposed degrees in phase from that previously considered. In other words, during the half cycle in which anodes 21 and 33 are positive, the lower end ofresistor I8 will be at a potential positive with respect to the upper end. Under these conditions, the potential of grid 8| is raised with respect to cathode 29 and the potential of grid 28 i is lowered with respect to cathode 23. When this happens, the voltage curve represented by line I9I of Figure 2 portrays the voltage applied to grid 32 of tube 22. Thus, assuming that the unbalance is exactly the same as shown in connection with the first six cycles, the tube 22 will become conductive during the first one of each six cycles. When it is so conductive, current will flow through the following circuit to electromagnetic winding I2: from the upper terminal of alternatlng current generator 96 through conductors I82 and I95, field winding I2, conductor 2III, anode 33, cathode 29, and conductors 88, 88, 82, I81, I63, I30, I3I, 91, I98, and I88. The result of the establishment of'this circuit is that the electromagnetic winding I2 is energized so that the other clutch is now engaged. As a result, the motor I8 rotates the shaft I4 in the opposite direction so as to move control device I8 in the opposite direction and to rotate contact arm I6 in the counterclockwise direction. Such counter-clockwise rotation of contact arm I8 will tend to rebalance the bridge in the manner previously considered. Thus, when contact arm I8 assumes a position corresponding to the position of contact 48, the bridge will be rebalanced so that both tubes 2| and 22 will again become nonconductive.

In the case of the unbalance of the bridge in either direction, it is obvious that the magnitude of the alternating component of the grid voltage 181 will depend upon the magnitude of unbalance. Thus, if the bridge is unbalanced to a greater degree than that Just considered, the axis of the alternating current voltage will be exactly the same but the maximum peak value will be considerably higher. Such a condition is illustrated in connection with the last two cycles of Figure 2 in which the unbalance is suflicientiy great that both of the first two cycles are conductive ones. As previously explained, the unbalance voltage is still sumciently small that the third cycle will not be a conductive one so that the tube in question will be conductive only two out of every six cycles. 11 this unbalance voltage is increased sufllciently as to cause the grid voltage to exceed the cut-oi! voltage at the beginning of the third voltage cycle, it will be obvious that the tube in question will be conductive during the first three'out of each six cycles. Under extreme conditions, the unbalance of the bridge will rise to a value in which the grid voltage will always exceed the cut-off potential. Under these conditions, the tube will a be conductive during the entire time.

As the bridge balance is restored, however, the tube will be conductive during smaller and smaller portions of the total number of cycles with the result that the speed 01 shaft 14 will be correspondingly reduced. Thus, provision is made for operating the controller at a relatively rapid speed when the unbalance is great and for operating it at a.

slow speed as balance is approached. With the arrangement described, it is possible to have an extremely sensitive system wherein the motor adjusts the position of the control device upon very slight changes in the value of the controlling condition.

Species of Figure 3 The species oi Figure 3 is substantially similar to that of Figure 1 with the exception that the change in biasing voltage exists for an entire cycle 01' the grid voltage rather than being changed for very brief intervals as in Figure 1. Furthermore, provision is made for increasing the grid voltage gradually through a maximum value and then gradualy decreasing it. In view of the fact that much of the apparatus of Figure 3 is identical to that of Figure 1, it is believed unnecessary to describe this apparatus again. The same numerals have been applied to Figure 3 to elements identical in function to those of Figure 1, and it is believed that by a comparison oi Figures 1 and 3, these portions of Figure 3 will be obvious without further description.

A rotary contactor 210 is secured to a shaft 181 leading from the reduction gear train 100. This rotary contactor 2111 comprises an outer and an inner track with which cooperate brushes 211 and 212. The outer conductive track consists of a continuous metal strip 214. The inner conductive track consists of a plurality of segments 215, 216, 211, 218, 218, and 220, each of these segments being separated from each other by insulating material. A resistance element 221 extends between conductive segments 2 I 5 and 2 I 6 and is connected thereto. A second resistance element 222 is connected between segments 216 and 211. A third resistance element 223 is connected between segment 211 and a conductive terminal 224 which extends through the insulating segment adjacent to it and is connected by a conductor 225 to the outer conductive memher 214. A resistor member 228 corresponding the terminal 224 and segment 218. Likewise, a resistor member 221 is connected between segments 218 and 219. A sixth resistor member 228 is connected between segments 219 and 220. As the contactor 210 is rotated in a counter-clockwise direction, the brush 212 will successively engage contact segments 220, 219, and 218. Whenthe brush 212 is in engagement with segment 220, the brush 212 is connected to brush 211 by contact segment 221i, resistors 228, 221, and 226, terminal 224, conductor 225, conductive strip 214 and brush 211. In other words, the three resistors 228, .221 and 226 are connected in series between brushes 212 and 211. When the disk has moved to a point where brush 212 engages segment 2 I 9, the circuit between brushes 212 and 211 will include only resistors 221 and 228. When the brush 212 engages segment 218, only resistor 222 will be included. Upon further rotation of the contactor 2111 in a clockwise direction, the brush 212 successively engages segments 211, 216, and 215. Upon engagement of segment 211, the resistor remains the same because of resistor 223 being connected in series between segment 211 and brush 211. Upon brush 212 engaging segment 216, resistors 222 and 223 are connected in series between brushes 211 and 212. When the contactor has rotated still further until brush 212 is in engagement with segment 21!, resistors .221, 222 and 223 will all be connected between brushes 211 and 212. It is believed that it will be obvious from the preceding paragraphs that upon continuous rotation of contactor 210, the amount of resistance between brushes 212 and 211 is decreased in three steps and is then increased in three steps, this cycle being repeated for each revolution of the contactor.

A rheostat is indicated by the reference numeral 240. This rheostat comprises a resistor 241 and slidable contact 242. The rheostat is connected between brushes 211 and 212 by con-' ductors 243, 244 and 245. The left-hand portion of resistor 241 will thus be connected in parallel with the resistance units 221 to 228 and 226 to 228, previously considered.

A resistor 255 is connected directly to the negative terminal of battery 93. The resistor 255 and battery 93 are connected between the center tap otthe resistor 10 and conductor 82 by the following circuit: from tap 90 through conductor 156, resistor 265, battery 93, and conductors 163 and 161 to conductor 82. It will be recalled that conductor 82 is connected to the two cathodes and that center tap 90 is conductively connected to the two grids. Hence, the biasing voltage will be determined by the voltage introduced by the circuit Just traced. This circuit includes the voltage of battery 93 which is fixed minus the potential drop across resistor 255. The amount or this potental drop depends upon the current flow through resistor 255. The rheostat 240 and the various resistors introduced by contactor 210 are connected in series with battery 93 and resistor 255. Thus, considering the rheostat 240, a circuit may be traced through resistor 241 of rheostat 240 as follows: from the positive terminal of battery 93 through conductor's 91. 198, 258, and 244, the left-hand portion of resistor 241, conductor 259 and resistor 255 to the left-hand terminal of the battery 83. As previously indicated, the various portions of resistors 221 to 223 and 228 to 228 are connected in parallel with resistor 241 depending upon the position of the contactor 2|0. Thus, a variable current will flow through resistor 255 depending upon the position of contactor 2"). This variable current flow will produce a variable potential drop across resistor 255' and will hence vary the voltage introduced between tap 90 and conductor 82. As previously indicated, this voltage is the amount of bias which is introduced between the grids and the cathodes.

Operation From the foregoing description, it will be apparent that as the contactor 2|0 is rotated, the

grid bias is changed in steps. This operation is shown graphically in Figure 4 in which the reference numeral I is employed to designate the potential existing between the anode and cathode of the tubes. The reference numeral |1| indicates the potential of the grid of the tube being considered. The numeral |l2 indicates that portion of the potential of the grid due to the biasing voltage.

Considering first the condition when brush 2|2 is in engagement with segment 220, the resistors 228, 221 and 226 will be connected in series between brushes 2|2 and 2. In other words, the maximum amount of resistance will be in the circuit between brushes 2 and H2 and hence in parallel with the left-hand portion of resistance 2 with rheostat 240. This will reduce the current flow through resistor 255 to a minimum so that the voltage drop across resistor 255 opposing the battery 93 will be at a minimum with the result that the bias on the grids of the tubes will be at a maximum. This condition is indicated in connection with the first cycle of plate voltage.

As soon as the contactor Zlli has rotated to a position such that brush 2|2 is in engagement with segment 2|9, only the resistors 22! and 225 will be connected between brushes 2 and 2|2-. This will effectively reduce the resistance in parallel with the left-hand portion of resistance grid voltage is increased in steps and is relatively 2M and will increase the current flow through resistor 255. This will increase the potential drop across resistor 255 and decrease the amount of the biasing voltage. In other words, the poten tial oi the grid, upon the segment 220 moving out of engagement with and segment 220 moving into engagement with brush 2|2 will be abruptly raised. This condition is illustrated in Figure 4 in connection with the second cycle of plate voltage. This potential of the grid will be maintained until the brush engages segment 2|8.

When segment 2|! moves into engagement with brush 2|2, only resistor 226 will be in parallel with the left-hand portion of resistor 2 so that the current flow through resistor 255 will again be abruptly increased. This, in turn, will efiect a further decrease in the biasing voltage, or in other words, an increase in the grid potential. The grid will remain at the new value when brush 2|2 is engaged by segment 2|! and until brush 2|2 has engaged segment 2| 5. This condition of the grid potential is illustrated in Figure 4 in connection with the intermediate two cycles. It will be noted that during these cycles, with the unbalance voltage at the value shown in Figure 4, the tube is conductive during both cycles.

When segment 2 8 moves into engagement with brush N2, the grid potential will again be decreased due to the fact that resistors 222 and 223 are both connected in parallel with resistor 2. This condition is illustrated in connection with the fifth cycle in Figure 4. When the segment 2|5 constant over any one cycle of grid voltage. It will be obvious that if desired, the number of cy-' cles of plate voltage involved in any one series might be increased. Thus. the grid voltage might be progressively increased over six cycles and decreased over a succeeding six cycles. Further: more, each value of grid potential might be maintained over several cycles instead oi' over only one cycle. i 1

In the foregoing description of the operation, no circuits have been traced in connection with the operation when one or the other of the tubes 2| and 22 is rendered conductive. It is believed that this is unnecessary since the circuits are all identical to those considered in connection with Figure 1. It will be obvious that upon either tube being rendered conductive a circuit is established to one of the clutch windings |2 or I3 so as to cause the controlling device |5 to be driven in one direction or the other until the bridge circuit has been rebalanced.

Conclusion It will be seen that I have provided a motor controlling apparatus making possible a motor control system of extreme sensitivity in which a motor is operated one direction or the other upon extremely slight variations in the controlling voltage. I

While I have shown certain specific embodiments of my invention, it is to be understood that this is only for purposes of illustration and that my invention is to be limited solely by the scope of the appended claims.

I claim as my invention:

1. In combination; an electronic amplifier having an input circuit and an output circuit; means for applying a controlling voltage to said input circuit;' and means for applying a variable biasing voltage to said input circuit; said last named means comprising a source of power and an impedance connected in said input circuit; resistance means; and switching means operable periodically to connect different portions of said resistance means in parallel with said source of power and'said impedance to vary by different amounts the magnitude of said biasing voltage, said biasing voltage being at all times suflicient to prevent said amplifier from being conductive it said controlling voltage is below a predetermined value.

2. In combination; an electronic amplifier having an input circuit and an output circuit; means for applying a controlling voltage to said input circuit; and means for applying a variable biasing voltage to said input circuit; said last named means comprising a unidirectionalsource of power and an impedance connected in said input circuit, resistance means, and switching meansorerable first to connect successively decreasing portions of said resistance means in parallel with said source of power and said impedance and then to connect successively increasing portions of said re-; sistance means in parallel with said source o cyclically varying at the same frequency as said output voltage and having a variable efifective value, means for applying to the control element electronic discharge devices each having a control element for controlling the discharge thereof, each of said devices being adapted to control the current flow through a diiIe'rent one of said two current paths. means for applying a cyclically varying voltage to the output terminals of said devices, means for applying a biasing voltage to the control elements or both discharge devices, impedance means connected to both control elements, and meansior applying to said impedance means a cyclically varying voltage in such a manner that said voltage simultaneously opposes the biasing voltage in connection with one control element and aids the biasing voltage in connection with the other depending upon its phase, and means for periodically decreasing the magnitude of said biasing voltage so as to increase the potential of the grid during predetermined positive cycles 01 said output voltage.-

4. In a motor control system. a motor means,

an electronic discharge amplifier having an output circuit controlling the operation or said motor means. said amplifier comprising a control element for controlling the discharge thereof, means for applying a cyclically varying voltage to said output circuit, a source of cyclically varying signal voltage having a variable efiective value, means for applying to the control element oi said discharge amplifier a cyclically varying input voltage including said signal voltage, and timer means for periodically increasing the magnitude of said input voltage during only predetermined cycles of said output voltage by amounts sufilcient to render said amplifier conductive in the event of at least a small signal voltage from said source but insufilcient to render said amplifier conductive in the absence oi such a signal voltage,

5. In a motor control system, a motor means, an electronic discharge amplifier having an output circuit controlling the operation or said motor means, said amplifier comprising a control element for controlling the discharge thereof, means for applying a cyclically varying voltage to said output circuit, a source of cyclically varying signal voltage having a variable efiective value, means for applying to the control element of said discharge, amplifier a cyclically varying input voltage including said signal voltage, timer means for periodically increasing the magnitude of said input voltage during only predetermined cycles of said output voltage by amounts sufiicient to render said amplifier conductive in the event of at least a small signal voltage from said source but insufilcient to render said amplifier conductive in the absence of such a signal voltage, and means associated with said timer means for causing a progressive change in the increase in the value of said input voltage during successive cycles of said output voltage.

6. In a motor control system. a motor means, an electronic discharge amplifier having an output circuit controlling the operation of said moof said discharge amplifier a cyclically varying input voltage including said signal voltage, and timer means for periodically increasing the magnitude of said input voltage during only predetermined cycles of said output voltage by amounts sufilcient to render said amplifier conductive in the event of at least a small signal voltage from said source but insufiicient to render said amplifier conductive inthe absence of such a signal voltage.

7. In a motor control system, a motor means, an electronic discharge amplifier having an output circuit controlling the operation of said motor means, said amplifier comprising a control element for controlling the discharge thereof, means for applying a cyclically varying voltage to said output circuit, means including an impedance network for providing a cyclically varying signal voltage varying in phase and magnitude with the relative values of the impedances of said network, a source of biasing voltage, means for applying to the control element of said discharge amplifier a cyclically varying input voltage including said signal voltage and said biasing voltage, and timer means for periodically increasing the magnitude of said input voltage during only predetermined cycles of said output voltage by amounts sufiicient to render said amplifier conductive in the event of at least a small signal voltage from said source but insuflicient to render said amplifier conductive in the absence of such a signal voltage.

8. In a motor control system, a motor means, an electronic discharge amplifier having an output circuit controlling the operation of said motor means, said amplifier comprising a control element for controlling the discharge thereof, means for applying a cyclically varying voltage to said output circuit, a source of cyclically varying signal voltage having a variable efiective val- ,ue, a source of unidirectional biasing voltage,

means for applying to the control element of said discharge amplifier a cyclically varying input voltage including said signal voltage and said biasing voltage. and timer means for periodically decreasing the magnitude of said biasing voltage during only predetermined cycles of said output voltage by progressively changing amounts, the largest decrease of which is sufficient to render said amplifier conductive in the event of at least a small signal voltage from said source but insuiiflcient to render said amplifier conductive in the absence of such a signal voltage.

9. In a motor control system, a motor means.

an electronic discharge amplifier having an output circuit controlling the operation of' said motor means, said amplifier comprising a control element for controlling the discharge thereof, means for applying a cyclically varying voltage to said output circuit, a source of cyclically varying signal voltage having a variable efiective value, a source of unidirectional biasing voltage. means for applying to the control element of said discharge amplifier a cyclically varying input voltage including said signal voltage and said biasing voltage, and timer means for periodically decreasing the magnitude of said biasing voltage during only predetermined cycles of said output voltage by progressively increasing and then decreasing amounts, the largest decrease of which is sufiicient to render said amplifier conductive in the event of at least-a small signal voltage from said source but insufilcient to render said ampli fier conductive in the absence oi such a signal voltage.

10. In a motor control system, a motor means, an electronic discharge amplifier having an output circuit controlling the operation of said motor means, said amplifier comprising a control element for controlling the discharge thereof, means for applying a cyclically varying voltage to said output circuit, a source of cyclically varying signal voltage having a variable eflectlve value, means for applying to the control element of said discharge amplifier a cyclically varying input voltage including said signal voltage, and means for increasing the magnitude of said input voltage during a portion oi the cycles of said output voltage by progressively changing amounts, the greatest of which is suilicient to render said amplifier conductive in the event or at least a small signal voltage from said source but insuf- 20 ficient to render said amplifier conductive in the absence of such a signal voltage. said last-named means comprising circuit connections associated with said control element, a plurality of resistors, and contactor means for selectively connecting different of said resistors in said circuit connections during different cycles of said output voltage.

11. In combination, a gaseous electronic discharge amplifier having an output circuit and a control element for controlling the discharge 18 through said amplifier and hence the now of current in said output circuit, means for applying a cyclically varying voltage to said output circuit, means for applying to the control element of said discharge amplifier a cyclically varying in put voltage including a cyclically varying signal voltage having a variable effective value, and timer means for periodically increasing the magnitude of said input voltage during only predetermined cycles of said output voltage by amounts sui'ilcient to render said amplifier conductive in the event of at least a small signal voltage but insufilcient to render said amplifier conductive in the absence of such a signal voltage.

SIEGF'RIED G. ISSERSTEDT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,164,728 Wey July 4, 1939 2,080,250 Bedford May 11, 1937 2,272,714 Lamb Feb. 10, 1942 2,169,294 Scull Aug. 15, 1939 2,047,984 Riggs Jul 21, 1936 1,960,350 Shackleton et al. May 29, 1934 1,977,256 Swart Oct. 16, 1934 30 1,867,398 Cockerell July 12, 1932 

